Although the notebook contained very little about cobalt-60 because it appears that Grimmett had a separate notebook for cobalt-60, what is in the notebook about cobalt-60 is of interest and is described in this chapter. He investigated the transmission characteristics of cobalt-60 γ-rays for various materials. Of special interest was concrete of various densities as a building material for the new hospital, and tungsten as material used for the cobalt unit. This required that he determine the density of the tungsten alloy to be used, which is described. Sometime in 1950, he received a 2 Ci cobalt-60 source, and his first task was to measure the exact strength of the source. Also there was an indication that the ionization chamber he used was not open to the atmosphere, and he set up an experiment using the source, a pump and a manometer to check it out. Although the results were preliminary and he wanted to repeat the experiment, the chamber was open to the atmosphere and giving correct readings. Of special interest was the fact that he found radioactive contamination on the outside of the source, which was not cobalt-60. He found that the contamination contained a short half-life (2.04 h) and a low-energy component, but no further information was given.